甲烷氧化偶联制C_2催化剂的研究进展(一)

本文话细地介绍了甲烷氧化偶联制备C_2的催化剂研究概况,并着重分析了催化剂的种类及其特性。     

Catalytic Performance of Coal Char for the Methane Reforming Process

A new concept of combined coal gasification and methane reforming in a single reactor was proposed as an alternative path for syngas production using coal and coalbed methane. Here, the results of this process are summarized. The experimental work was carried out in a fixed‐bed reactor. Methane cracking, CO₂/steam reforming of methane over coal char, and the effects of chars made from different types of parent coal on methane conversion were examined. The catalytic effect of coal char on methane cracking and reforming increased with decreasing coalification degree. A synergistic effect was observed in that, while the coal char catalyzed the methane reforming reactions, gasification of the coal char took place simultaneously, which counter‐balanced the deposition of carbon especially for the methane‐steam‐char system.     

A Critical Assessment of Li/MgO-Based Catalysts for the Oxidative Coupling of Methane

Li/MgO is one of the most frequently investigated catalysts for the oxidative coupling of methane. Besides catalytic testing, it is also a suitable system to perform surface science experiments and quantum chemical calculations, which is not possible for many other active catalysts. However, the real structure of Li/MgO, the nature of the active center and the structure - activity relationship remain unclear, despite all the research that has been done. The aim of this review is to summarize the available knowledge on Li/MgO to structure and accelerate and improve the ongoing work on this catalytic system.     

Investigation of Coking During Dry Reforming of Methane by Means of Thermogravimetry

Coking dynamics of Ni‐based and Ni‐free catalysts were studied in a magnetic suspension thermobalance under methane dry reforming conditions. Ni‐rich catalysts undergo strong coking featured with a surface saturation point where the coking rate is drastically reduced. Catalyst resistance towards coking may be enhanced by using noble‐metal‐based Ni‐free precursors or decreasing the Ni content in the catalytic system. The post reaction performed temperature‐programmed oxidation experiment of the coked catalyst is diffusion‐limited due to large amounts of formed carbon.     

Combined Single-pass Conversion of Methane Via Oxidative Coupling and Dehydro-aromatization

A single-pass process with the combination of oxidative coupling (OCM) and dehydro-aromatization (MDA) for the direct conversion of methane is carried out. With the assistance of the OCM reaction over the SrO–La₂O₃/CaO catalyst loaded on top of the catalyst bed, the duration of the dehydro-aromatization reaction catalyzed by a 6Mo/HMCM-49 catalyst shows a significant improvement, and. the initial deactivation rate constant of the overall process revealed about 1.5×10⁻⁶ s⁻¹. Up to 72 h on stream, the yield of aromatics was still maintained at 5.0% with a methane conversion of 9.6%, which is obviously higher than that reported for the conventional MDA process with single catalyst. Upon the TPR results, this wonderful enhancement would be attributed to an in-situ formation of CO₂ and H₂O through the OCM reaction, which serves as a scavenger for actively removing the coke formed during the MDA reaction via a reverse Boudouard reaction and the water gas reaction as well.     

Combined Single-Pass Conversion of Methane Via Oxidative Coupling and Dehydroaromatization

A new reaction mode, i.e., the combined single-pass conversion of methane via oxidative coupling (OCM) over mixed metal oxide (SLC) catalysts and dehydroaromatization (MDA) over Mo/HZSM-5 catalysts, is reported. With the assistance of an OCM reaction over SLC catalysts in the top layer of the reactor, the deactivation resistance of Mo/HZSM-5 catalysts is remarkably enhanced. Under the selected reaction conditions, the CH₄ conversion decreased from 18 to 1% and the aromatics yield decreased from 12.8 to 0.1%, respectively, after running the reaction for 960min on both 6Mo/HZSM-5 and SLC-6Mo/HZSM-5 catalyst system without O₂ in the feed. On the other hand, for the SLC-6Mo/HZSM-5 catalyst system with O₂ in the feed, the deactivation was improved greatly, and after 960min onstream the CH₄ conversion and aromatics yield were still as high as 12.0 and 8.0%, respectively. The promotion effect mainly appears to be associated with in situ formation of CO₂ in the OCM layer, which reacts with coke via the reverse Boudouard reaction.     

甲烷二氧化碳干气重整催化剂研究进展

甲烷二氧化碳干气重整催化剂的研究,对天然气资源的综合高效利用和环境保护具有重要意义。简述了CH_4-CO_2重整反应的机理,从活性组分、载体、助剂、制备方法等方面,综述了国内外CH_4-CO_2干气重整催化剂的研究进展,并从反应机理上分析了催化剂失活的原因。研究表明,提高催化剂活性组分对CO_2的吸附能力、制备微小晶粒孔隙发达的催化剂是消除催化剂表面积炭的有效方法。     

SrTiO3超细微粒的制备与甲烷氧化偶联催化性能

采用溶胶－凝胶法合成钙钛矿型立方相SrTiO3超细微粒,探讨了成胶温度,配体,溶剂以及干凝胶热处理条件对生成SrTiO3微粒粒度,均匀性及比表面积的影响,用TGA－DTA,IR,TEM,XRD,XPS,BET表面积测试等手段对SrTiO3超细微粒的形成机制,结构及形貌和甲烷氧化偶联催化性能进行了研究,发现SrTiO3超细微粒对于甲烷低温（~650℃）氧化偶联催化性能明显优于固相反应法制备的大粒子SrTiO3催化剂。     

Coupling and reforming of methane by means of low pressure radio-frequency plasmas

Non-oxidative coupling of CH₄/H₂ mixtures was carried out by means of radio frequency (rf) glow discharges for the first time. A central composite design was employed to determine the best experimental conditions for methane transformation into higher hydrocarbons and to fit the experimental data. rf power was the factor showing the highest effect on the results while CH₄/H₂ mole ratio showed the lowest. Conversion was 46.4% at 100 W, 0.07 mbar and CH₄/H₂ mole ratio of 1/2. Selectivity was 56.9% for C₂, 6.9% for C₃, and 36.2% for C₄ hydrocarbons. Least squares fits of quadratic equations yielded approximating functions permitting to predict results of random experiments with errors of about 5%. The same rf system was used for the reforming of methane with CO₂, O₂, and steam plasmas, respectively. The highest oxidation was observed with oxygen whilst steam plasma produced the best results. H₂/CO mole ratio was adjusted by setting specific experimental parameters of the latter. CO₂ free synthesis gas was produced at higher H₂O and CH₄ flow rates, i.e. 0.8 mmol/h and higher power, i.e. 100 W. CO₂ and CO free H₂ was produced at 0.3 and 0.6 mmol/h flow rates of H₂O and CH₄, respectively, and 50 W.     

Combination of Sorption-Enhanced Steam Methane Reforming and Electricity Generation by MCFC: Concept and Numerical Simulation Analysis

Abstract

Reformed gas made by the steam methane reforming(SMR) process is used as fuel feed to MCFC, but it is not as good as pure hydrogen due to the presence of CO₂ and CO. The sorption-enhanced steam methane reforming(SE-SMR) process can reduce CO₂ and CO to a low level and produce high purity hydrogen. Considering the merits of similar operating temperatures (about 500°C) and carbon dioxide recycle, a novel concept of a six-step sorption-enhanced steam methane reforming (SE-SMR) combined with electricity generation by molten carbonate fuel cell (MCFC) is proposed. In the present paper, a cycle of the SE-SMR process, which include the steps of reaction/adsorption, depressurization, gas purges (nitrogen and reformed gas, respectively), and pressurization with reformed gas, is modeled and analyzed. The process stream in the SE-SMR process is used as anode feed in MCFC. According to the result of numerical simulation, a fuel cell grade hydrogen product (above 80% purity) at the SE-SMR temperature of 450°C can be obtained. A carbon dioxide recycle mechanism is developed for cathode feed of MCFC from flue gas by burning with excess air to achieve a proper CO₂/air ratio (about 30:70). The novel electricity generation system, which can operate at lower energy consumption and high purity hydrogen feed is helpful for the MCFC'S performance and life time.     

Analysis of Membrane Reactors for Integrated Coupling of Oxidative and Thermal Dehydrogenation of Propane

This study presents strategies capable to intensify the thermal dehydrogenation of propane (TDH) using integrated reactor concepts. An inert packed bed membrane reactor for distributed dosing of oxygen to realize the oxidative dehydrogenation (ODH) was studied and compared to a reactor with catalytically active membrane. The latter concept allows to combine TDH and ODH in one apparatus to overcome the chemical equilibrium by in situ conversion of the by‐product H₂ using O₂ or in a reverse water‐gas shift reaction by CO₂. If CO₂ is used as active sweep gas the reactor offered better performance regarding yield and selectivity. Strategies for further thermal integration are discussed.     

Effect of Electronic Properties of Catalysts for the Oxidative Coupling of Methane on Their Selectivity and Activity

The oxidative coupling of methane (OCM) to higher hydrocarbons may eventually become an interesting alternative for the chemical utilization of natural gas. Extensive studies have been conducted since the works of Keller and Bhasin [l] and of Hinsen and Baerns [2].     

Effect of Electronic Properties of Catalysts for the Oxidative Coupling of Methane on Their Selectivity and Activity

The oxidative coupling of methane (OCM) to higher hydrocarbons may eventually become an interesting alternative for the chemical utilization of natural gas. Extensive studies have been conducted since the works of Keller and Bhasin [l] and of Hinsen and Baerns [2].     

Bismuth-Containing Oxides as Catalysts for Oxidative Coupling of Hydrocarbons

Some bismuth-containing oxides, such as bismuth molybdates, are known to be effective catalysts for so-called allylic oxidation of C₃-C₄ olefins including partial oxidation to unsaturated aldehyde, oxidative dehydrogenation to diolefin, and ammoxidation to corresponding nitrile. This type of catalyst is well studied and repeatedly reviewed [1-3]. Its high effectiveness can be interpreted within a dual-site concept according to which hydrocarbon adsorbs on an active site associated with one of the metal oxide components while oxygen adsorbs on an active site associated with another metal oxide component. For instance, the authors [4, 5] assume a bismuth center to be responsible for the hydrocarbon conversion to an allylic species which then reacts further at a molybdenum site to produce aldehyde.     

Simulating and Optimizing Auto-Thermal Reforming of Methane to Synthesis Gas Using a Non-Dominated Sorting Genetic Algorithm II Method

Conventional synthesis gas production plants consist of a natural gas steam reforming to CO + 3H₂ on Ni catalysts in a furnace. An alternative method for highly endothermic steam reforming is auto-thermal reforming. In this work, synthesis gas production by auto-thermal reforming was simulated based on a heterogeneous and one-dimensional model in two cases. The first case was the auto-thermal reformer of Dias and Assaf's study. The present work was validated by the reported experimental results. The second case was the fixed-bed catalytic auto-thermal reactor operated at high pressure, which was suitable for methanol production and Fischer–Tropsch reactions (baseline case). Then, the effect of operating variables on the system behavior was studied. Finally, Pareto-optimal solutions were determined by non-dominated sorting genetic algorithm II. The objectives included obtaining a H₂/CO ratio of 2 in the produced synthesis gas and the maximum methane conversion. The adjustable parameters were the feed temperature, mass flux, and O₂/CH₄ and H₂O/CH₄ ratios in the feed.     

Tuning the Performance of Ni‐Based Catalyst by Doping Coinage Metal on Steam Reforming of Methane and Carbon‐Tolerance

Density functional theory (DFT) calculations are employed to investigate the key reactions in steam reforming of methane (SRM) on Ni‐based bimetallic surface alloys, including the dissociation of CH₄ and H₂O, the oxidation of CH by oxygen atom to form formyl (CHO), and the dehydrogenation of CHO to form carbon monoxide (CO). The aim of this investigation is to hunt for an optimal catalyst for SRM, which can inhibit carbon formation while maintaining high activity to the SRM. Coinage metal impurity (Au, Ag, and Cu) doped Ni catalysts have been proven to inhibit carbon deposition. In this work, we focus on investigating the doping effects on some leading processes in SRM. It is found that the coinage metal doping has a little effect on the two‐step dissociation of H₂O, which has a linear correlation between the dissociation barriers and the OH–H coadsorption energies. In addition, the dehydrogenation of CHO is kinetically favorable on all alloy surfaces. However, for the CH oxidation to CHO, only the Ni–Cu surface remains high activity. These results suggest that Ni–Cu bimetallic material is an excellent active carbon‐tolerance SRM catalyst for solid‐oxide fuel cells.     

A Comparative Study of Hydroxyapatite- and Alumina-Based Catalysts in Dry Reforming of Methane

The dry reforming of methane over hydroxyapatite- and alumina/magnesia (commercial Pural MG 30)-supported nickel catalysts was investigated. The catalytic performance of the catalysts prepared with fresh supports highly depended on the basicity, the metal-support interaction, and the metal particle size. Calcination of the supports at 1200 °C for 5 h made the catalysts less active because of specific surface area reduction and basicity destruction. However, this treatment allowed avoiding any further catalyst deactivation by thermal sintering and maintained excellent catalytic stability over 300 h of time-on-stream. These tests under simulated industrial conditions (high contact time and long time-on-stream) showed the competitiveness of the prepared catalysts in this important catalytic process.     

Two‐Dimensional Model for Oxidative Coupling of Methane in a Packed‐Bed Membrane Reactor

A two‐dimensional (2D) model of a packed‐bed membrane reactor was developed to describe ethylene production by oxidative coupling of methane (OCM). The model covers all relevant energy and mass transport processes in the reactor and allows a more precise prediction of the temperature and conversion patterns. It is demonstrated that the fast OCM reaction leads to oxygen depletion in the vicinity of the membrane, causing strong radial concentration gradients in the bed. Further results indicate that the detailed 2D model can provide more accurate predictions of experimental data than the simplified one.     

Preparation of a LaNiO3/γ‐Al2O3 Catalyst and its Performance in Dry Reforming of Methane

LaNiO₃/γ‐Al₂O₃ catalysts containing 10, 15, 20, and 25 wt % Ni were prepared by a combination of sol gel with propionic acid as solvent and an impregnation method (LNA‐acid) as well as with ethanol as solvent and addition of acetic acid (LNA‐eth). Catalytic activities towards CO₂ reforming of CH₄ were tested in a fixed‐bed reactor at 700 °C, 750 °C, and 800 °C. LNA‐eth with 20 wt % Ni exhibited the best activities in dry reforming of methane and a good activity and stability, when it was tested at 800 °C during 75 h time‐on‐stream.     

A Novel Design Studies for the Mono-Block Ceramic Filter by the Coupling Mode Analysis

This paper was focused on design automation and introduced a novel design method, called coupling mode analysis (CMA), to determine an exact pattern for the target values of the mono-block ceramic filter to be designed. To get the exact dimensions of planar passive parameters on the ceramic block, new mapping method of the pattern was used on the basis of the coupled resonance modes between the resonator and either added capacitors of inductors. To verify this approach, the monoblock band pass filter (M-BPF) with two poles was designed and fabricated. The measured results show that the center frequency, bandwidth, and attenuation pole frequency of the BPF are closely agreed with the designed values using the CMA method.